Catheters are used in a wide variety of minimally-invasive or percutaneous medical procedures. One type of catheter is an intravascular catheter, which enables a physician to remotely perform a medical procedure by inserting the catheter into the vascular system of the patient at an easily accessible location and navigating the tip of the catheter to the target site. Using catheter-based methods, many internal sites may be remotely accessed through the patient's vascular system or other body lumen structure.
In some applications, a needle may be connected to a catheter assembly to deliver a therapeutic agent into remote sites within a patient's body. For example, in a percutaneous myocardial revascularization procedure, the inside surface of the heart is accessed by an intravascular catheter via a retrograde route through the venous system. A needle is advanced through the catheter, and the heart muscle is then injected with therapeutic agents, such as stem cells or drugs, to promote new blood vessel formation in the heart muscle.
When using an injection catheter, the depth of needle penetration into the tissue is important because the therapeutic agent may require delivery at a precise depth and/or because excess needle penetration may cause injury to the tissue. However, because the needle is not visible to the physician, it can be difficult to determine the penetration depth of the needle. In some cases, the physician can estimate the penetration depth of the needle by the distance the needle has been advanced through the catheter. However, when the catheter takes a tortuous path through the vascular system, for various reasons related to the bending and curving of the catheter, the distance in which the needle has been advanced proximally is not necessarily equal to the distance the needle has traveled from the distal tip of the catheter. Therefore, it is desirable to provide feedback that indicates the actual distance in which the needle has been advanced from the distal tip of the catheter.